Means for mounting bumpers on rectilinear energy absorbers

ABSTRACT

Bumper mounting brackets provide for rectilinear transmission of thrust from the bumper to a rectilinear energy absorber, and enable relative angular, rocking freedom of movement to minimize lateral or bending strains on the absorber. The brackets have rectilinear rigidity and impact resistance, coupled with resilient yieldability for accommodating relative angular impact displacements of the bumper with respect to the absorber.

United States Patent McLauchlan 451 N 20, 1973 [54] MEANS FOR MOUNTINGBUMPERS ON 2,610,881 9/1952 Schuettpelz 293/70 RECTILINEAR ENERGYABSORBERS 2,917,264 12/1959 Hartenstein.... 248/358 R 1,516,916 11/1924Dougherty 1. 188/8 Inventofl J McLauchlan, Royal 2,244,353 6/1941 Zaiger293/66 Mich.

[73] Assignee: Houdaille Industries, Inc., Buffalo, PrimaryExaminerGerald M. Forlenza I N. Y. Assistant Examiner-Robert Saifer i 1Filed Sept. 1971 Attorney-Carlton Hill et al.

[21] Appl. No.. 180,740 ABSTRACT '52 US. Cl. 293/99 248/204 bracketsPmvide rectilinear 51 1111. C1. Br 19/02 bumper a [58] Field of Search248/ 204 358 R- energy absmbe" enable "elative angular mkmg 267/133,293/1 Dlq 2 DIG g 65 freedom of movement to minimize lateral or bending70 85 E 87 6 strains on the absorber. The brackets have rect1l1nearrigidity and impact resistance, coupled with resilient [56] ReferencesCited yieldability for accommodating relative angular impactdisplacements of the bumper with respect to the UNITED STATES PATENTSabsorben 2,845,144 7/1958 Bohn 188/1 C 2,227,560 7 1/1941 Szabo 293/8614 Claims, 7 Drawing Figures PMENTEUnnv P0 1915 SHEEI 10F INVENTOR.Jay/v Mal/40044 AW.

BY DEL jg ,6 @MTTORNEYS PMENTEUHUV20 m5 3.773.373 sum 20F uar- INVENTOR.JO/L/A/ McZ/l 00 /4 M from at least minor collisions involvingautomotive vehicle bumpers, in particular, such as may occur at as lowas 3 mph. to about m.p.h. impact of one vehicle relative to another,where the bumpers are mounted in an essentially fixed or rigid mannerrelative to the vehicle frame, it has been proposed to mount thesebumpers on or in association with rectilinear energy absorbers enablingyielding of the bumpers towards the vehicle frame in a manner to preventor-at least substantially alleviate damage. Such absorbers may be of theso-called direct acting or telescopic type on the order of shockabsorbers commonly employed in vehicle suspensions and having not onlytelescopic energy absorbing capability, but also return or recoverycapability such that after a collapsing, telescoping stroke, theabsorber will automatically return to normal extended condition.

A disadvantage heretofore encountered in employ ment of telescopicabsorbers in bumper mountingshas resided in necessarily extremeresistance to bending or lateral distortion of such absorbers throughouttheir length, whereas impact against bumpers is rarely encountered in amanner which will assure straight-in displacement of the bumper freefrom any canting. This results from the fact that the bumpers have aconsiderable horizontal length-against any portion of which the impactmay. be focused or concentrated'such that there is a greater tendency toyield inwardly of the impacted portion of the bumper where the point ofimpact is other than dead center, i.e., directly aligned with the axisof the vehicle. To alleviate this problem, it has been proposedto'provide pivotal connections between the bumper and absorber or atleast one endof the absorber and either the bumper or the'frame, or atboth ends, and associate the absorber with-primary support andimproved-bumper mounting bracketstructure for efficientutilization ofrectilinear energy absorbers in bumper supportsystems.

A further object of the invention is to provide new and improvedlow-cost, efficient, durable, reliable means formountingbumpers inassociation with rectili'nearenergyabsorbers and-enabling not onlyrectilinear but also canted displacement of the bumper relative to theassociate supporting structure, without binding or stressing theabsorber.

Yet another object of the invention is to provide a new and improvedbumper mounting bracketistr'ucture having rectilinear rigidity as wellas resilient flexibility capability adapting the same especially for,use in mounting automotive vehicle bumpers oniand in associationwithsupporting rectilinear energy absorbers.

Other objects, features and advantages of the invention will be readilyapparent from. the followingdescription of certain preferred embodimentsthereof, taken in conjunction with the accompanying drawings, althoughvariations and modifications may be effeced without departing from thespirit and scope of the novel concepts embodied in the disclosure, andin which:

FIG. I is a fragmentary top plan view showing an assembly embodyingfeatures of the invention;

FIG. 2 is a sectional elevational view taken substantially along theline IIIl of FIG. 1;

FIG. 3 is a vertical sectional detail view taken substantially along theline III-III of FIG. 1;

FIG. 4 is a plan view of the bracket structure of FIGS. 1-3illustrating, schematically, certain functional characteristics;

FIG. 5 is a plan view of a modification of the bracket structure;

FIG. 6 is a plan view of another modification of the bracket structure;and FIG. 7 is a plan view of a' further modification. On reference toFIGS. l4, a bracket structure l0'according to the present invention isconstructed and arranged'to connect a bumper assembly 11 to arectilinear energy absorber 12 mounted on a support such as anautomotive vehicle frame 13. Construction of the bracket structure 10 issuch that together with the absorber 12, the bumper assembly 11 isadapted to be fully supported at one side of an associated vehicle frame13, and a duplicate or alochiral bracket structure and absorber areadapted to provide the full support for the bumper at the opposite sideof the vehicle frame 13 at the front or the rear of the vehicle or atboth places. Thereby, two of the bracket structures 10 and two of theabsorbers 12 will serve to support the bumper assembly 11 at properelevation and against upward or downward or transverse displacementrelative to the vehicle frame 13, but the absorber 12 will permit inwarddisplacement of the bumper toward the frame 13 in-response to pressuresor impacts of a magnitude which might otherwise damage the bumper or thevehistand jacking forces when the bumper is engaged by a lifting jack toelevate the associated vehicle. In addition', the bracket structure ispossessed of great linear rigidity for impact force transmission fromthe bumper assembly to the absorber, and ample torsional resilientflexibility for canting displacements of the bumper relative to thevehicle frame or to avoid binding of the absorber or shock isolatorduring shock or other impact induced inward displacements of the bumper.To this end, the bracket structure is preferably constructed as a pair.of identical bracket members 14 which cooperate in' mounted assemblyback-to-back. Each of the members l4-is desirably constructed ofresilient metal suitable for the intended bumper system. For example,0.090 to 0. l inch thick, heat-treated steel which will strongly resistcompressive forces, but is possessed of adequate resilience for theintended purpose, may be used, such as SAE 1074, heat-treated to.40l.46l Brinell. Where practicable merely work-hardened material ormaterial which is inherently possessed of the desired characteristicsmay be used. Desirably the material should lend-itself readily to simplestamping and forming process of manufacture. If preferred, a onepiecesection extruded orforged bracket structure may be employed possessingthe desirable attributes of the invention.

Each of the bracket members 14 may be constructed from a rectangularpiece of the material shaped to provide a straight body portion 15having at outboard end a right angularly extending flange 17 forattachment to the bumper l1, and at its inboard end a right angularflange 18 extending in the same direction as the flange l7 and parallelthereto and adapted for attachment to the absorber 12. For a typicalfront bumper system, the bracket members 14 may be about 4 inches wide,with the overall body length to the respective outer faces of theattachment flanges about to 3% inches, the bumper attachment flangeabout 4 inches in length and the absorber attachment flange about 1%inches in length.

In mounting the bracket 10, the bracket bodies 15 are placed incoextensive back-to-back abutment with the flanges 17 extending in acommon vertical plane in opposite horizontal directions and abutting avertical inwardly facing flange 19 of a horizontally extending box-beam20 reinforcing and carrying a bumper shell 21 of the bumper assembly 11.Attachment of the bracket flanges 17 is desirably effected by means ofrivets or bolts 22 extending through longitudinally elongated bolt holes23 in the flanges enabling optimum horizontal adjustment of the boltsrelative to the beam flange 19 in which the bolt holes are preformed anddimensioned in complementary diameter to the bolt shanks. An upperflange 20a of the reinforcing boxbeam may extend inwardly in overlyingprotective relation to the bracket 14.

Attachment of the bracket flanges 18 to the absorber 12 is effected bymeans of bolts 24 securing the bracket flanges to an outer end lateralattachment flange 25 on a reciprocable plunger 27 of the absorber whichnormally projects in protracted relation from a barrel 28 of theabsorber which carries on. its front end portion a mounting flange 29secured as by means of bolts 30 to a supporting L-shaped bracket flange31 attached in any suitable manner fixedly to the associated beam or barof the frame 13. To accommodate the barrel 28, the supporting bracketflange 31 has a clearance aperture 32 therethrough, with the mountingflange 29 resting against the outer face of the supporting bracketflange. Through this arrangement, inward displacement of the bumper 11effects inward stroking of the absorber plunger 27, with the barrelflange 29 and the bracket 31 holding the absorber barrel in fixedrelation to the frame 13.

In order to improve the rigidity of the bracket bodies 15 andreinforce'the same against impact distortion, each of the bracket bodiesmay be formed with a longitudinal rib 33 of substantial radiusprojecting in the same direction as the flanges 17 and 18 and extendinginto reinforcing relation to the juncture between one of the flanges andthe body. In the form of FIGS. l-4, the reinforcing rib extends acrossthe juncture between the bracket body 15 and the absorber attachmentflange l8 such that this juncture is quite rigid and there is strongresistance to any hinging at such juncture: On the contrary, at theopposite end of the bracket body 15 in each instance, the juncture-withthe attachment-flange enables resilient hingi'ng-movement of the'flan'ge relative to the body. Thus, where the reinforcing rib 33maintains the juncture with the flange'l8 rigid, the reinforcing ribterminates short of the juncture with the attachment flange 17 so thatresilient hing'in'g of the flange 17 relative to the body l5'is enabled.This feature is demonstrated in FIG. 4 where it will be obse'rved thatthe attachment flanges 17 of the bracketIO'are hingedly swingable inconcert as indicated in dash outline and in dot-dash outline so as toaccommodate canting of the bumper 11 relative to the absorber I2-which,of course, is held on a fixed axis through its mounting to the frame.Thereby, when the bumper is impacted to either side of the longitudinalaxis plane of the vehicle on which the bumper is mounted, so that thebumper ll cants as it is displaced inwardly, the inward component forceis efficiently transmitted by the bracket 10 straight onto the absorber12, while the flanges 17 rock or hinge to accommodate the cantedposition of the bumper, which will vary as bumper displacementcontinues. On return of the bumper to original position, the flanges 17due to their resilience readily return to their original position, andassist in returning the bumper to the desired transverse normal positionrelative to the associated vehicle.

Referring to FIG. 5, alternatively to having the mounting bracketflanges which are attached to the bumper assembly resiliently hingedlyflexible, the bracket flanges which are attached to the absorber may beresiliently hingedly flexible where that is deemed preferable or morefeasible. Where that arrangement is desired, the reinforcing rib 33 onthe body 15' of each of the bracket members 14 extends across thejuncture between the body and the bumper attachment flange 17 while therib terminates short of the juncture between the bracket body 15 and theabsorber attachment flange 18'. Thus, the flanges 18 of the bracketassembly 10 will be resiliently hingedly flexible about the joints asschematically indicated in FIG. 5.

Where the particular installation is deemed to require increased angularimpact resistance as well as excellent head-on impact resistance, themodification of FIG. 6 may be employed. Therein, the bracket assembly10" has, similarly as in the other forms, a pair of bracket members 14"set back-to-back, but with the body portions 15" divergently relatedfrom abutment at their inner or absorber attachment ends, or statedalternatively, extending obliquely from the bumper attachment flanges17" to abutment shoulders adjacent to the absorber attachment flanges18". In this instance the reinforcing ribs 33" are at the confrontingsides of the body portions 15" running to and reinforcing the junctureswith the flanges 17", but extending short of the junctures with theflanges 18" and in shouldering abutment at their ends adjacent to theflanges 18''. It will be understood thatthe flanges 18" will have thesame canting ability as the flanges 18' in FIG. 5 by virtue of theresilient hingingflexibility of the junctures betweenthe body portions15" and the flanges 18".

In FIG. 7 is shown a form of the invention which is especially suitablefor use where the available space between the outboard end of theabsorber and the bumper is extremely limited such as from about 34inches to 1% inches. To this end, a bracket structure 35 comprisessimilar bracket members 37 which may be formed heavy gauge sheetmetal-members having their planes disposed vertically in assemblybetween a bumper and an absorber and each provided with a body 38 formedon a radius and joining with respective outboard bumper attachmentflanges 39 and respective inboard absorber-attachment flanges 40. Inthis instance the outboard flanges 39 are of substantially greaterlength than the inboard flanges 40 and have horizontally elongatedrespective attachment bolt slots 41. Means are provided on the shorterinboard flanges 40 for bolt-on attachment to the absorber, desirablycomprising so-called clinch nuts 42 permanently affixed to the outboardsides of these flanges which are suitably apertured for the purpose. Byhaving the bracket member backs 38 arched toward one another inengagement, extremely rigid mutual support I is provided againstdeformation by inboard impact forces which are thus efficientlytransmitted from the bumper through the bracket structure to theabsorber. On the other hand at least the outboard flanges 39 are enabledto respond resiliently flexibly to relative canting of the bumper withrespect to the absorber.

As will be observed, in all forms of the bracket means for mounting thbumper on rectilinear energy absorbers, the bracket body and flangeshave great resistance to deformation in their planes, and by orientingthose planes in a vertical direction in an automobile bumper, jackingforces or other forces tending to effect roll are thoroughly resisted.Nevertheless, canting of the bumper about a vertical axis during inwarddisplacement due to impact is efficiently accommodated by the hingingcapability of at least certain of the attachment flanges of the bracketstructure. Thereby not only is impact force efficiently transmitted fromthe bumper by the bracket structure to the energy absorber, but theenergy absorber is relieved from undue transverse or bending stressesduring energy absorbing stroking thereof.

It will be understood that variations and modifications may be effectedwithout departing from the spirit and'scope of the novel concepts ofthis invention.

I claim as my invention:

1. In a mounting for a bumper on a rectilinear energy absorber:

' a force transmission bracket structure connected to and between thebumper and the energy abosrber and comprising a body rigidly resistiveto impact forces and respective flanges angular tothe body and havingmeans for attachment to the bumper and to the energy absorber;

at least'one of said flanges being resiliently hingedly flexiblyconnected to the body to enable canting of the bumper while under impactdisplacement toward the energy absorber;

said bracket structure comprising a pair of heavy gauge sheet metalmembers each having a body portion and respective bumper and energyasborber attachement flanges;

said body portions being in back-to-back engagement and with saidflanges of the respective members extending in respectively oppositedirections; and said body portions having longitudinally extendingreinforcing ribs.

2. In a mounting according to claim 1, said reinforcing ribs extendingthrough junctures with certain of the flanges and extending short ofothers of the flanges.

3. In a mounting according to claim 2, said body portions extending in.{straight back-to-back relation throughout their lengths and said ribsprojecting away from the backs ofthe body portions. 1

'4. In a mounting according to claim 2, said body por tions beingdivergently related, and said ribs projecting from the backs of the bodyportions and joining in shouldering relation at one of their ends.

5. In a mounting for a bumper'o'n a rectilinear energy absorber:

a force transmission bracket structure connected to and between thebumper and the energy absorber and comprising a body rigidly resistiveto impact forces and respective flanges angular to the body and havingmeans for attachment to the bumper and to the enerby absorber;

said bracket structure comprising a pair of formed heavy gauge metalmembers each of which has a body portion with the body protions adaptedto be placed in back-to-back relation and saidattachment flanges beingat the respective opposite ends of said body portions and extending awayfrom the backs of the body portions; and

each of said bodyportions having a respective longitudinally extendingreinforcing rib which runs I through and reinforces the .juncture of thebody portion with one of said flanges and extends short of the other ofsaid flanges, whereby the juncture with said other of said flangesserves as a resilient hinge enabling hinging flexure of said other ofsaid flange relative to the body portion. 6. In combination with ahorizontal bumper having an inboard side and generally rectilinearabsorber means supported in outboard projecting relation on a supportingstructure and having a limited range of stroking movement relativethereto:

connecting bracket structure comprising rigid body means extending toand between said inboard side of the bumper and said absorber means;

attachment flange means on both ends of said body means attached torespectively the bumper and said absorber means;

the flange means at least at one end of the body means being resilientlyhingedly flexible relative to the body means to accommodate canting ofthe bumper relative to the absorber means while displacing inwardly onimpact which drives the bumper inboard toward the absorber means;

said bracket structure comprising members having body portionscomprising said body means and said body portions and said flange meansbeing of substantial width and oriented with their planes vertical;

said body portions having longitudinally extending reinforcing ribswhich run in reinforcing relation through the junctures with the bodyportions of the flange means located on the opposite ends of the bodyportions of each of the members, and said ribs extending short of theflange means at said one end of the body portions whereby the juncturesof said one end flange means with the body portions permit resilienthinging flexing of said one end flange means relative to the rigid bodyportions.

7. In a mounting for a bumper on a rectilinear energy absorber:

a force transmission bracket structure connected to and between thebumper and the energy absorber and comprising a body rigidly resistiveto impact forces and respective flanges angular to the body and havingmeans for attachment to the bumper and to the energy absorber;

at least one of said flanges being resiliently hingedly flexiblyconnected to the body to enable canting of the bumper while under impactdisplacement toward the energy absorber;

said bracket structure comprising a pair of heavy gauge sheet metalmembers each having a body portion and respective bumper and energyabsorber attachment flanges;

said body portions being in back-to-back engagement and with saidflanges of the respective members extending in respectively oppositedirections; and

rib means stiffly reinforcing said body portions.

8. In a mounting according to claim 7, said reinforcing means comprisingribs formed on said body portions and projecting away from the backs ofthe body portions.

9. In a mounting according to claim 7, said reinforcing means extendingto and including the remaining of said flanges to thereby reinforce thejuncture between said remaining of the flanges and the bodysubstantially rigidly against flexing.

10. In a mounting according to claim 9, said reinforcing meanscomprising ribs on said body portions projecting away from the backs ofthe body portions.

11. In a combination with a horizontal bumper having an inboard side andgenerally rectilinear absorber means supported in outboard projectingrelation on a supporting structure and having a limited range ofstroking movement'relative thereto:

connecting bracket structure comprising rigid body means extending toand between said inboard side of the bumper and said absorbermeans;attachment flange means on both ends of said body means attached torespectively the bumper and said absorber means;

the flange means at least at one end of the body means being resilientlyhingedly flexible relative to the body means to accommodate canting ofthe bumper relative to the absorber means while displacing inwardly onimpact which drives the bumper inboard toward the absorber means;

said bracket structure comprising members having body portionscomprising said body means and said body portions and said flange meansbeing of substantial width and oriented with their planes vertical; and

longitudinally extending reinforcing rib means on said body portions.

12. In a combination according to claim 11, said reinforcing rib meansextending short of the flange means at said one end of the body portionsand running in reinforcing relation through the junctures with the bodyportions of the flange means located on the opposite ends of the bodyportions of each of the members whereby substantially to stiffen againstflexing.

13. In a combination according to claim 12, said reinforcing meanscomprising central longitudinally extending n'bs formed on said bodyportions and across said junctures with the flanges at said oppositeends of the body portions.

14. In a combination according to claim 11, said reinforcing meanscomprising central longitudinally extending ribs formed on said bodyportions.

1. In a mounting for a bumper on a rectilinear energy absorber: a forcetransmission bracket structure connected to and between the bumper andthe energy abosrber and comprising a body rigidly resistive to impactforces and respective flanges angular to the body and having means forattachment to the bumper and to the energy absorber; at least one ofsaid flanges being resiliently hingedly flexibly connected to the bodyto enable canting of the bumper while under impact displacement towardthe energy absorber; said bracket structure comprising a pair of heavygauge sheet metal members each having a body portion and respectivebumper and energy asborber attachement flanges; said body portions beingin back-to-back engagement and with said flanges of the respectivemembers extending in respectively opposite directions; and said bodyportions having longitudinally extending reinforcing ribs.
 2. In amounting according to claim 1, said reinforcing ribs extending throughjunctures with certain of the flanges and extending short of others ofthe flanges.
 3. In a mounting according to claim 2, said body portionsextending in straight back-to-back relation throughout their lengths andsaid ribs projecting away from the backs of the body portions.
 4. In amounting according to claim 2, said body portions being divergentlyrelated, and said ribs projecting from the backs of the body portionsand joining in shouldering relation at one of their ends.
 5. In amounting for a bumper on a rectilinear energy absorber: a forcetransmission bracket structure connected to and between the bumper andthe energy absorber and comprising a body rigidly resistive to impactforces and respective flanges angular to the body and having means forattachment to the bumper and to the enerby absorber; said bracketstructure comprising a pair of formed heavy gauge metal members each ofwhich has a body portion with the body protions adapted to be placed inback-to-back relation and said attachment flanges being at therespective opposite ends of said body portions and extending away fromthe backs of the body portions; and each of said body portions having arespective longitudinally extending reinforcing rib which runs throughand reinforces the juncture of the body portion with one of said flangesand extends short of the other of said flanges, whereby the juncturewith said other of said flanges serves as a resilient hinge enablinghinging flexure of said other of said flange relative to the bodyportion.
 6. In combination with a horizontal bumper having an inboardside and generally rectilinear absorber means supPorted in outboardprojecting relation on a supporting structure and having a limited rangeof stroking movement relative thereto: connecting bracket structurecomprising rigid body means extending to and between said inboard sideof the bumper and said absorber means; attachment flange means on bothends of said body means attached to respectively the bumper and saidabsorber means; the flange means at least at one end of the body meansbeing resiliently hingedly flexible relative to the body means toaccommodate canting of the bumper relative to the absorber means whiledisplacing inwardly on impact which drives the bumper inboard toward theabsorber means; said bracket structure comprising members having bodyportions comprising said body means and said body portions and saidflange means being of substantial width and oriented with their planesvertical; said body portions having longitudinally extending reinforcingribs which run in reinforcing relation through the junctures with thebody portions of the flange means located on the opposite ends of thebody portions of each of the members, and said ribs extending short ofthe flange means at said one end of the body portions whereby thejunctures of said one end flange means with the body portions permitresilient hinging flexing of said one end flange means relative to therigid body portions.
 7. In a mounting for a bumper on a rectilinearenergy absorber: a force transmission bracket structure connected to andbetween the bumper and the energy absorber and comprising a body rigidlyresistive to impact forces and respective flanges angular to the bodyand having means for attachment to the bumper and to the energyabsorber; at least one of said flanges being resiliently hingedlyflexibly connected to the body to enable canting of the bumper whileunder impact displacement toward the energy absorber; said bracketstructure comprising a pair of heavy gauge sheet metal members eachhaving a body portion and respective bumper and energy absorberattachment flanges; said body portions being in back-to-back engagementand with said flanges of the respective members extending inrespectively opposite directions; and rib means stiffly reinforcing saidbody portions.
 8. In a mounting according to claim 7, said reinforcingmeans comprising ribs formed on said body portions and projecting awayfrom the backs of the body portions.
 9. In a mounting according to claim7, said reinforcing means extending to and including the remaining ofsaid flanges to thereby reinforce the juncture between said remaining ofthe flanges and the body substantially rigidly against flexing.
 10. In amounting according to claim 9, said reinforcing means comprising ribs onsaid body portions projecting away from the backs of the body portions.11. In a combination with a horizontal bumper having an inboard side andgenerally rectilinear absorber means supported in outboard projectingrelation on a supporting structure and having a limited range ofstroking movement relative thereto: connecting bracket structurecomprising rigid body means extending to and between said inboard sideof the bumper and said absorber means; attachment flange means on bothends of said body means attached to respectively the bumper and saidabsorber means; the flange means at least at one end of the body meansbeing resiliently hingedly flexible relative to the body means toaccommodate canting of the bumper relative to the absorber means whiledisplacing inwardly on impact which drives the bumper inboard toward theabsorber means; said bracket structure comprising members having bodyportions comprising said body means and said body portions and saidflange means being of substantial width and oriented with their planesvertical; and longitudinally extending reinforcing rib means on saidbody portions.
 12. In a combination according to claim 11, saidreinforcing rib means extending shOrt of the flange means at said oneend of the body portions and running in reinforcing relation through thejunctures with the body portions of the flange means located on theopposite ends of the body portions of each of the members wherebysubstantially to stiffen against flexing.
 13. In a combination accordingto claim 12, said reinforcing means comprising central longitudinallyextending ribs formed on said body portions and across said junctureswith the flanges at said opposite ends of the body portions.
 14. In acombination according to claim 11, said reinforcing means comprisingcentral longitudinally extending ribs formed on said body portions.